Endometriosis, the third leading cause of gynecologic hospitalization in the United States, remains one of the most enigmatic gynecologic pathologies. Defined by the presence of endometrial tissue outside of the uterine cavity, these implants respond to the hormonal cues of the menstrual cycle and "bleed" as they would in the uterus. The consequence is the development of adhesions, scarring, and painful inflammation. Signs and symptoms include dysmenorrhea, dyspareunia, infertility, dysuria, and dyschezia. The effects of the disease can be physically and mentally debilitating with frequent misdiagnoses and poor treatment options. Its prevalence among U.S. women has been estimated to be approximately 10%. Despite the high morbidity and health care cost associated with endometriosis, the etiology has not been fully delineated, and no modifiable, protective risk factors have been identified. Dietary factors have been the focus of a growing number of endometriosis patient-initiated books and web sites, with a chapter in a new book from the Endometriosis Association dedicated to diet choices and "prevention" of endometriosis. Unfortunately, few studies to date have directly evaluated the relation between diet and endometriosis. Using data on 1,500 laparoscopically confirmed incident cases of endometriosis collected from the Nurses' Health Study II, an ongoing, prospective cohort study that began in 1989, we propose a study to assess the following three hypotheses: a) Women who consume greater amounts of omega-6 fatty acids, saturated fats, and trans fats are at greater risk of endometriosis; b) Women who consume smaller amounts of omega-3 fatty acids, monounsaturated fats, and fiber are at greater risk of endometriosis; and c) Women whose diets are lower in vitamins B6 and magnesium -- via foods or supplements -- are at greater risk of endometriosis. All analyses will control for other known and suggested risk factors for endometriosis such as body mass index, oral contraceptive use, and cigarette smoking. We will have substantial power to evaluate the above hypotheses. These analyses will be the first to evaluate the relation between these dietary factors and this important and understudied cause of morbidity among premenopausal women. [unreadable] [unreadable]